1. Field of the Invention
This invention relates to a semiconductor device capable of emitting light and provided with a reflector for the light. More particularly, it relates to a semiconductor device, such as a light-emitting diode, used for backlighting a push button in a small electric device such as a portable telephone.
2. Description of the Related Art
Small electronic devices such as portable telephones have been widely used lately because of their handiness. Needless to say, portable telephones are provided with a number of push buttons operated for making a call or performing other functions. The push buttons of a recent portable telephone may be backlit by small light sources, so that the user can operate the device even in the dark. For the light source, use may be made of an LED (light-emitting diode).
FIGS. 12 and 13 show a conventional light-emitting diode provided with a reflector. As illustrated, the conventional diode Y is constituted by a rectangular base unit 1xe2x80x2, an LED chip 3xe2x80x2 mounted on the unit 1xe2x80x2 and a casing 5xe2x80x2 enclosing the LED chip 3xe2x80x2.
The base unit 1xe2x80x2 is composed of an insulating substrate 1Axe2x80x2, a first electrode 2Axe2x80x2 and a second electrode 2Bxe2x80x2. The electrodes 2Axe2x80x2 and 2Bxe2x80x2, which are electrically insulated from each other, extend from the upper surface 10xe2x80x2 of the substrate 1Axe2x80x2 onto the lower surface 12xe2x80x2 through a side surface 11xe2x80x2. The electrodes 2Axe2x80x2 and 2Bxe2x80x2 have upper portions 2axe2x80x2 and 2bxe2x80x2, respectively, which extend on the upper surface 10xe2x80x2 of the substrate 1Axe2x80x2. These electrodes 2Axe2x80x2, 2Bxe2x80x2 may be made by etching a conductive metal layer formed on the substrate 1Axe2x80x2.
The LED chip 3xe2x80x2 is arranged on the upper portion 2axe2x80x2 of the first electrode 2Axe2x80x2 and is electrically connected thereto. The top surface 30xe2x80x2 of the LED chip 3xe2x80x2 is electrically connected to the upper portion 2bxe2x80x2 of the second electrode 2Bxe2x80x2 via a wire 4xe2x80x2 made of gold for example.
The casing 5xe2x80x2 is formed with a cavity 50axe2x80x2, defined by an inner wall surface 5axe2x80x2 of the casing 5xe2x80x2. As shown in FIGS. 12 and 13, the cavity 50axe2x80x2 is made in the form of a reversed, truncated cone extending through the thickness of the casing 5xe2x80x2. Thus, when the casing 5xe2x80x2 is mounted on the substrate 1Axe2x80x2, the LED chip 3Axe2x80x2 and the wire 4xe2x80x2 are disposed in the cavity 50axe2x80x2. 
As shown in FIG. 13, the inner wall surface 5axe2x80x2 is covered with a metal film 5bxe2x80x2 formed by sputtering or vacuum evaporation. The metal film 5bxe2x80x2 is rendered reflective so as to work as a light-reflecting member or reflector. As illustrated, the cavity 50axe2x80x2 is filled up with transparent resin 50xe2x80x2 (such as epoxy resin) which is highly permeable to light. The resin 50xe2x80x2 will be referred to as the xe2x80x9clight-permeable portionxe2x80x9d below.
With the above arrangement, part of the light emitted from the LED chip 3Axe2x80x2 is reflected by the metal layer 5bxe2x80x2 before getting out of the light-permeable member 50xe2x80x2, while the other part of the emitted light passes through the light-permeable member 50xe2x80x2 without being reflected by the metal layer 5bxe2x80x2. As a result, a light beam having a generally cylindrical form is emitted from the light-permeable member 50xe2x80x2.
As stated above, the light-emitting diode Y, which is usable as a backlight for a push button of a portable telephone, is arranged to emit a generally cylindrical light beam. On the other hand, the push buttons of a portable telephone are often made in a non-circular form (e.g. elliptical or rectangular). Under these circumstances, the light-emitting diode Y fails to properly brighten the entirety of a push button. This shortcoming may be overcome by using more than one light-emitting diode Y for illuminating a single push button. However, it is clear that such a solution will disadvantageously lead to a cost increase.
It is, therefore, an object of the present invention to provide a semiconductor device which is capable of properly backlighting a non-circular push button of an electronic device.
According to the present invention, there is provided a semiconductor device comprising:
a substrate provided with a first electrode and a second electrode formed thereon;
a semiconductor chip mounted on the substrate for emitting light, the semiconductor chip being electrically connected to the first electrode and the second electrode; and
a reflector enclosing the semiconductor chip for reflecting the light emitted from the semiconductor chip;
wherein the reflector has an elongated transverse section.
The elongated transverse section may be oblong, elliptical, rhombic, or rectangular.
According to a preferred embodiment of the present invention, the reflector may have a first vertical section defining a quadric curve.
Further, the reflector may have a second vertical section intersecting the first vertical section at right angles. The second vertical section may define a quadric curve.
The reflector may define a quadric surface tapering toward the semiconductor chip.
According to a preferred embodiment of the present invention, the semiconductor chip may be a light-emitting diode chip.
According to another preferred embodiment, the semiconductor chip may be a laser diode chip.
The semiconductor device of the present invention may further comprise a casing supported by the substrate. The casing may be provided with an inner surface defining a cavity, wherein the inner surface serves as the reflector.
Preferably, the casing may be made of a reflective material.
Preferably, the casing may be white.
Preferably, the casing may be made of a polycarbonate resin containing titanium oxide.
According to another preferred embodiment of the present invention, the semiconductor device may further comprise a casing supported by the substrate and a light reflecting film as the reflector. In this case, the casing may be provided with an inner surface defining a cavity, and the light reflecting film is formed on the inner surface.
Preferably, the light reflecting film may be made of metal.
Further, the light reflecting film may be white.
Preferably, the light reflecting film may be made of a polycarbonate resin containing titanium oxide.
The semiconductor device of the present invention may further comprise a light-permeable member, wherein the reflector defines a space accommodating the light-permeable member.
Preferably, the light-permeable member may be made of an epoxy resin.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.